The advent of central heating relegated the fireplace to a decorator's item. The relatively recently recognized reality regarding the long term uncertainty of the quality and cost of fossil fuels has necessitated a rethinking as to how the fireplace might be employed as at least a supplemental heat source.
The heat emanating from the fireplace may warm those sitting in close proximity thereto, and its radiant energy may tend to warm the immediate room, but the operating fireplace induces an air flow which reduces the overall heating efficiency of the primary heat source. So long as the fireplace is operating there is an endless trail of warm, expensive, household air racing up the chimney. For years no one objected. Energy to operate the central heating system was available in abundance, and at relatively low cost.
Gradually it became apparent that the world's fuel supplies do not issue forth from a cornucopia; rather, the supply is finite; some fuels, such as wood, can be replenished if its source is carefully husbanded, but overall the cost of fossil fuels has continued to rise. By the early 1970s the crunch was widely felt.
Many people boarded up their fireplaces; some closed and sealed the dampers to their fireplaces; and, others judiciously operated their fireplaces only on those days when the resultant overall loss of heat would not be sorely felt. This latter approach created the paradox of not being able to use the fireplace on truly cold days.
It is estimated that there are currently in excess of twenty million fireplaces in the United States, and with that available market the fireplace insert was developed. The fireplace insert converts the outmoded fireplace into a valuable, secondary heat source and still permits man the luxury of fulfilling the primordial instinct of watching a crackling fire while basking in its cozy warmth.
Currently, manufacturers are providing fireplace inserts in a wide variety of models. Initially, a self contained firebox was simply inserted into the old fireplace opening, and a shroud was was fitted between the insert and the facing of the original fireplace opening to minimize the undesirable exiting flow of warm air from within the home. However, this arrangement has two major drawbacks. Not only is an effective seal between the insert and the fireplace opening virtually impossible to effect, but such an arrangement inherently exposes the exhaust gases to an excessive surface area which serves to cool the exhaust gases, allowing them to condense and deposit creosote within the old fireplace as well as upwardly along the interior of the the chimney. Creosote deposits are a natural fire hazard and must be avoided.
Both drawbacks can be greatly minimized by the use of a positive interconnect system that extends between the exhaust vent of the fireplace insert and the flue liner in the chimney. Such positive interconnect systems, or at least portions thereof, have been employed, but they have heretofore been rather difficult to install and, if effective, have been sufficiently complicated as to be fairly costly.
Some of the more popular interconnect systems effect a positive connection only between the fireplace insert and the damper. In addition, however, it is highly desirable to provide a direct, enclosed flow path from the damper to the flue liner in the chimney. A smoke chamber is normally provided between the damper and the flue of the chimney, and the inclusion of an enclosed flow path therethrough can eliminate any tendency for creosote to be deposited on the walls of the smoke chamber. The enclosed flow path from the damper to the flue also tends to maintain a higher flue temperature, which serves to increase the draft action of the chimney, thereby further improving the performance of the insert.
The use of flexible, oval ducting has been widely suggested to effect the enclosed flow path between at least the damper and the flue liner, and while such an arrangement is not only theoretically quite effective but also very attractive in artists' renditions employed in sales brochures, the actual installation requires that such flexible ducting be bent in a generally S-shaped curve during installation. Chimney dimensions and layouts are not standard, and that precludes pre-shaping the ducting. In fact, the majority of chimney layouts even prevent the ducting from being shaped prior to insertion. As a result, the person who installs the flexible, oval ducting must attempt to bend the ducting after it has been at least partially inserted through the damper, and it must be appreciated that the person doing the work is then attempting to bend that portion already inserted. This is a difficult task, at best, and virtually impossible in some chimneys because of their interior configuration.